#!/usr/bin/env python3
# -*- coding: utf-8 -*-
"""
ambari_jinja2.visitor
~~~~~~~~~~~~~~

This module implements a visitor for the nodes.

:copyright: (c) 2010 by the Jinja Team.
:license: BSD.
"""

from ambari_jinja2.nodes import Node


class NodeVisitor(object):
  """Walks the abstract syntax tree and call visitor functions for every
  node found.  The visitor functions may return values which will be
  forwarded by the `visit` method.

  Per default the visitor functions for the nodes are ``'visit_'`` +
  class name of the node.  So a `TryFinally` node visit function would
  be `visit_TryFinally`.  This behavior can be changed by overriding
  the `get_visitor` function.  If no visitor function exists for a node
  (return value `None`) the `generic_visit` visitor is used instead.
  """

  def get_visitor(self, node):
    """Return the visitor function for this node or `None` if no visitor
    exists for this node.  In that case the generic visit function is
    used instead.
    """
    method = "visit_" + node.__class__.__name__
    return getattr(self, method, None)

  def visit(self, node, *args, **kwargs):
    """Visit a node."""
    f = self.get_visitor(node)
    if f is not None:
      return f(node, *args, **kwargs)
    return self.generic_visit(node, *args, **kwargs)

  def generic_visit(self, node, *args, **kwargs):
    """Called if no explicit visitor function exists for a node."""
    for node in node.iter_child_nodes():
      self.visit(node, *args, **kwargs)


class NodeTransformer(NodeVisitor):
  """Walks the abstract syntax tree and allows modifications of nodes.

  The `NodeTransformer` will walk the AST and use the return value of the
  visitor functions to replace or remove the old node.  If the return
  value of the visitor function is `None` the node will be removed
  from the previous location otherwise it's replaced with the return
  value.  The return value may be the original node in which case no
  replacement takes place.
  """

  def generic_visit(self, node, *args, **kwargs):
    for field, old_value in node.iter_fields():
      if isinstance(old_value, list):
        new_values = []
        for value in old_value:
          if isinstance(value, Node):
            value = self.visit(value, *args, **kwargs)
            if value is None:
              continue
            elif not isinstance(value, Node):
              new_values.extend(value)
              continue
          new_values.append(value)
        old_value[:] = new_values
      elif isinstance(old_value, Node):
        new_node = self.visit(old_value, *args, **kwargs)
        if new_node is None:
          delattr(node, field)
        else:
          setattr(node, field, new_node)
    return node

  def visit_list(self, node, *args, **kwargs):
    """As transformers may return lists in some places this method
    can be used to enforce a list as return value.
    """
    rv = self.visit(node, *args, **kwargs)
    if not isinstance(rv, list):
      rv = [rv]
    return rv
